As feature sizes continue to decline in modern photolithographic semiconductor manufacturing processes, effects, such as undesired line edge roughness, insufficient lithographical resolution, and limited depth of focus problems can increase. More particularly, photoresist image footprints may become increasingly difficult to control as semiconductor device features become smaller and closer together.
Adhesion promoters may be used to bond the photoresist to the semiconductor substrate or other device surface until the photoresist is exposed to light, thereby defining feature edges and boundaries within the device. Photoresist, however, may persist around the substrate surface and photoresist interface. This is because some regions toward the bottom of the photoresist may not become sufficiently soluble after being exposed to an incident radiation to be completely removed, and instead remain bonded to the substrate by the adhesion promoter. These areas of persisting photoresist may correspond to areas where an incident radiation signal is weakest due to radiation absorption by photoresist or reflective interaction effects between the substrate and photoresist.
A prior art technique for addressing the shortcomings of traditional adhesion promoters is the use of a photoactive adhesion promoter. Photoactive adhesion promoters contain photoacid generators (PAGs), which react to incident light by releasing acid in regions in which the photoresist is exposed to the light. The acid helps to remove the photoresist from these regions, thereby improving the accuracy of features defined by the presence of photoresist.
FIG. 1 illustrates a prior art photoadhesion promoter moiety comprising a PAG. The prior art example of FIG. 1 illustrates a system that is capable of attaching a PAG material to a semiconductor wafer as a self-assembled layer. The photoactive adhesion promoter of FIG. 1 comprises an adhesion promoter and a PAG. The PAG comprises a photon harvesting group and a catalyst group. In the embodiment illustrated in FIG. 1, the adhesion promoter is trimethoxysilane, the photon harvesting group is methyldiphenylsulfonium, and the catalyst group is nonafluorobutanesulfonate. In addition, a linker bonds the adhesion promoter to the photon harvesting group.
The adhesion promoter, photon harvesting group, and the catalyst group may comprise different compounds as well. For example, the adhesion promoter may comprise alkoxysilane, silylchloride (a subclass of silylhalide), phosphate, phosphonate, alkene, thiol, or sulfide.
The photon harvesting group may comprise sulfonium salts, such as triarylsulphonium. Triarylsulphonium is a general class, in which aryl represents any structure with an aromatic group bound to the sulfur atom as well as functionalized aryl groups where functionalization may be heteroatoms, such as fluorine, chlorine, bromine, and functional groups such as alcohol (OH), nitro (NO2), amine (R3N), amide (R2NC(O)R), carboxylic acid (RCOOH), ester (RCOOR), ether (ROR), carbonate (ROC(O)OR).
Furthermore, alkyldiarylsulfonium and dialkylarylsulfonium are a general class of sulfonium salts which may be used, in which aryl is defined as above and alkyl is a hydrocarbon group, such as (CH2)nCH3 where n=0 to 11, as well as functionalized hydrocarbon groups, in which functionalization may be heteroatoms, such as fluorine, oxygen, nitrogen, chlorine, bromine and functional groups such as alcohol (OH), nitro (NO2), amine (R3N), amide (R2NC(O)R), carboxylic acid (RCOOH), ester (RCOOR), ether (ROR), or carbonate (ROC(O)OR). Alternatively, the photon harvesting group may comprise iodonium salts, such as diaryl and alkyaryl, in which aryl and alkyl are as defined above.
The catalyst group may comprise alternative compounds, such as perfluoroalkylsufonate, alkylsulfonate, arylsulfonate, perfluoroalkyl, alkyl and aryl phosphate, or fluoroalkylsulfonamide.
Other photoadhesion promoters include sulfides, nitroaryl derivatives, or aryl sulfates (for example, tosylates). PAGs may include sulfide and onium type compounds such as diphenyl iodide hexafluorophosphate, diphenyl iodide hexafluoroarsenate, diphenyl iodide hexafluoroantimonate, diphenyl p-methoxyphenyl triflate, diphenyl p-tert-butylphenyl triflate, diphenyl p-isobutylphenyl triflate, diphenyl p-tert-butylphenyl triflate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroarsenate, triphenylsulfonium hexafluoroantimonate, bis-(t-butylphenyl)iodonium triflate, triphenylsulfonium triflate, triphenylsulfonium nonafluorobutylsulfonate, diphenyliodonium heptadecafluorooctylsulphonate, and dibutylnaphthysulfonium triflate, as well as the combinations and permutations of the above moieties.
Examples of photo-base generators (PBGs) may include nitrocarbamate or quaternary ammonium dithiocarbamate and other generators described in, for example, Prog. Polym. Sci., volume 21, 145 (1996 Elsevier Science, Ltd.) or in J. Polym. Sci. Part A: Polym. Chem., 39, 1329-1341 (2001).
Sacrificial light absorbing material (SLAM) is typically used to fill holes or trenches in the surface of various semiconductor material (e.g. substrate material) before subsequent processing layers are added. Furthermore, SLAM materials are useful in that they absorb incident light, thereby reducing the effect of sporadic photoresist destruction that can result from light reflected from the material exposed to the light. SLAM is typically spun on to a wafer material and later etched, leaving SLAM in the holes or trenches within the surface in order to create a relatively smooth surface.
FIG. 2 illustrates a prior art dual damascene process, in which a photoresist layer (including a PAG) and a SLAM layer are deposited on a semiconductor surface. A mask layer can be applied, exposing the photoresist layer to incident radiation (ultra-violet light, extreme ultra-violet light, electron beam, x-ray, etc.) in areas that are not covered by the mask layer, removing photoresist from the exposed areas.
Prior art processing techniques typically require at least two processing steps to apply a PAG (typically contained within the photoadhesion promoter of the photoresist) and a SLAM to the wafer. This is because the PAG is typically included in the photoresist, which is applied after the SLAM. Using extra process step or steps to apply PAG and SLAM to a wafer can be costly in terms of processing time and wafer yield, as these steps require time and serve as a potential source of defects within the process.
Furthermore, prior art semiconductor processing techniques, such as those used in a damascene process flow, typically require a bake step, in which the wafer can be heated to extreme temperatures. During a bake, the wafer and SLAM may become porous, allowing amines to be released from the silicon material in the wafer, which can get trapped within a superjacent ILD layer and/or migrate ‘upward’ to the photoresist layer.
FIG. 2 illustrates the migration path of amines released from the wafer that get trapped in the ILD and then migrate up to the photoresist layer. The amines trapped in the ILD can flow through the SLAM and react with an overlying photoresist layer, thereby deteriorating (“poisoning”) the photoactive properties of the photoresist. Resist poisoning can result in a photoresist residue that cannot react with incident light, and therefore remains after the photoresist is developed, causing features within the semiconductor device to be deformed.